linux-kernel - Re: [PATCH 0/3] fix GART to respect device's dma

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Message-Id: <20080916222032O.fujita.tomonori@lab.ntt.co.jp>
Date:	Tue, 16 Sep 2008 22:20:40 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	andi@...stfloor.org
Cc:	fujita.tomonori@....ntt.co.jp, mingo@...e.hu, joerg.roedel@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] fix GART to respect device's dma_mask about
 virtual mappings

On Tue, 16 Sep 2008 02:54:32 +0200
Andi Kleen <andi@...stfloor.org> wrote:

> FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> writes:
> 
> > Currently, gart IOMMU ignores device's dma_mask when it does virtual
> > mappings. So it could give a device a virtual address that the device
> > can't access to.
> 
> Huh? That is what the need_iommu() logic in gart_map_sg()
> does. An I'm not aware of any bugs in this area.

What the need_iommu() does is seeing if GART needs to do virtual
mappings or not.

(After need_iommu() checking) What this patchset does is to guarantee
that GART provides a virtual address that a device can access to.


> Did you actually see that failure in practice? I don't see
> how it could happen.

No, I did not. This patchset does the right thing theoretically, I
think, but if such problem never happens for GART, I'll drop the patch
for GART. Joerg?
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